The development of multi-pulse common rail injection systems in which fuel injectors are actuated to provide pilot and/or post injections as well as the primary or main injection has prompted the need for new, end-of-the-line, functional test equipment that can measure the fuel injected by the fuel injector.
While positive displacement systems connected to a highly accurate electronic displacement measuring system are sufficiently accurate to measure multi-pulse common rail injection systems, they are typically very complex and expensive. Consequently, such positive displacement, piston type measurement systems, are not suitable for use in the manufacturing assembly line environment where numerous systems are required to test a significant number of fuel injectors.
Alternative methods to expensive positive displacement systems connected to highly accurate electronic displacement measuring systems have the advantage of being rugged and applicable to the manufacturing or remanufacturing line environment. However, such measurement systems are not designed to measure fueling in multi-pulse common rail injection systems. In particular, such measurement systems are not adapted to measure the amount of fuel injected during pilot and/or post injections, as well as the primary injection.
An example of an alternative method to positive displacement includes a common-rail fuel injection rate measurement system consisting of a pressure chamber with pressure sensors, an amplifier box, an output processing unit, a data processing unit, and a volumetric flow-meter. The system also includes a back pressure sensor, a temperature sensor, a back pressure relief valve, and a discharge valve.
However, such known systems require complex processing and filtering of captured sensor output to derive information regarding the fuel injection quantity, variation, and/or rate shape. Such filtering and complex processing is necessary to remove the noise in the acquired data caused by the fuel pressure pulses reflected within the system.
Unfortunately, developing such extensive filters and processing methods is expensive. Furthermore, filtering and processing sensor output can decrease the accuracy of the system since the quality of the filters and methods used to process the sensor data can render the results inaccurate. Often, the resolution of the apparatus is not able to resolve the microsecond difference between the twin rate peaks of a multi-pulse common rail injection system.
Therefore, what is needed is a testing apparatus and method which is relatively inexpensive and capable of rendering accurate readings in both single and multi-pulse common rail injection systems.